There are two modes for driving organic EL display devices, namely, the passive matrix mode and the active matrix mode. The active matrix mode is being the leading mode among the driving modes. This trend is particularly remarkable in the field of large-size display devices.
In general, pixels of active matrix organic EL display devices each have, for each organic EL element, a switching transistor for transmitting data signals and a drive transistor for driving an organic EL element in response to each data signal transmitted by the switching transistor (for example, see Patent Document 1). There occurs parasitic capacitance between these members disposed on each pixel and wiring layers such as a scanning line and a signal line. In order to suppress display failure called crosstalk due to this parasitic capacitance, a method is disclosed in which an electric field pattern is disposed so as to serve as an electric field shield for a scanning line and a signal line (for example, see Patent Document 2).
If the drive transistors of the respective pixels are driven by the same gate voltage even though the drive transistors of the respective pixels have different threshold voltages, current values supplied from the drive transistors to the organic EL elements vary, resulting in non-uniform display. In order to solve this problem, methods are known in which area-gradation expression or time-division-gradation expression is performed based on digital gradation driving. In the case of analog gradation driving, a method is disclosed in which variations in the threshold voltages of the drive transistors are detected and a so-called compensation circuit, which compensates for the variations, is formed in each pixel (for example, see Patent Document 3).
Patent Document 1: JP 2006-47999 A
Patent Document 2: JP 2006-30635 A
Patent Document 3: JP 2005-31630 A